Mixing of various materials, for example paint, has heretofore been effected by manually mixing or agitating the material, such as by stirring or shaking, or by mechanically reproducing these activities. For example, U.S. Pat. No. 3,894,723 is directed to a mechanical agitator, while U.S. Pat. Nos. 1,908,561 and 3,265,366 are exemplary of patents disclosing paint shaking devices. The mixing action is relatively slow and inefficient in these devices. Material shaking devices, such as paint shakers, require substantial mechanical structure and a heavy base or anchoring since vibration is a major problem. Due to vibration and the force of the material on the lid of the container, cumbersome clamping apparatus must be employed to tightly retain the lid in position during the shaking operation. U.S. Pat. Nos. 2,599,833 and 2,894,309 teach clamping apparatus for use with containers in shaking devices.
Others have proposed mixing by accelerating material in a container first in one direction and then in the opposite direction to achieve mixing by the combination of shear forces and the creation and destruction of the vortex in the material. A mixer of this type is shown in U.S. Pat. No. 3,542,344. While a mixer of this type reduces the problems of vibration and eliminates the necessity to clamp the lid on the container, substantial power and braking apparatus are required to effect the acceleration and reversal of the material in the container. Another type of mixer spins the container in one direction and oscillates the container at the same time. An example of this type of device is disclosed in U.S. Pat. No. 3,181,841. This type of device also requires substantial mechanical structure, disadvantageously causes vibration and requires clamping of the lid or cover of the container. Still another type of mixing apparatus simultaneously spins a container of material about two perpendicular axes. U.S. Pat. No. 3,880,408 discloses a device in which the container is rotated continuously about the two axis, whereas U.S. Pat. No. 3,706,443 discloses apparatus which rotates the container continuously about one axis but only rocks about the second, perpendicular axis by gyroscopic forces due to imbalance in the system. While the resulting mixing action is relatively rapid, considerable mechanical structure, often requiring a gimbal arrangement is required and vibration and the necessity to clamp the lid to the container are still encountered.
Thus, various types of apparatus have been proposed to accomplish the mixing of material rapidly and efficiently, but none of the proposed or heretofore used devices have been able to accomplish this goal without requiring substantial mechanical structures, inordinate power consumption, and/or structure to overcome or lessen the effects of vibration and forces acting upon the lid of a container.
Therefore, there is a need for an improved material mixing device of relatively simple mechanical design which can attain efficient mixing action, including bottom-to-top mixing action with low power consumtion, with very little vibration and without the need to clamp the lid to the container.